interner just uses uints, not idents with syntax context

also, move interner fns out of parser_testing
remove unused cx's
rand example fixup
fixing interner function names
added fresh-name fn
remove interner from tt_reader
remove interner field from string_reader
removed unused imports (and one unused argument)
remove unused get_ident_interner's
moved TLS of sctable to ast_util, hid parameter in hygiene calls
tmp
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